Printing plates



SePt- 10, 1963 @,s. BRAZNELL ETAL 3,103,168

PRINTING PLATES Filed March 19, 1962A United States Patent O 3,103,168PRINTING PLATES George Stuart Braznell, Frontenac, and Ralph E.McIlvaney, St. Louis County, Mo., assignors to Braco Engraving Co., St.Louis, Mo., a corporation of Missouri Filed Mar. 19, 1962, Ser. No.180,472. 3 Claims. (Cl. 10b-40.1.1)

This invention relates to methods of making rubber printing plates, 'andmore particularly to a method of making what may be referred to as amade-ready rubber printing plate.

It rwill be understood that `a rubber printing pil-ate essentiallycomprises a rubber plate having on one face thereof a pattern in reliefof the matter which is to be printed by means of the plate. When apattern includes both large printing Iareas `and small printing areas(such as fine lines or dots, for example), it is usually necessary inorder to obtain a proper impression in the printing operation thatprovision be made `for applying less pressure on the small areas thanthe large areas, otherwise, if sufficient pressure is applied Lforproper impression of the larger areas, the small areas will beundesirably distorted. Heretofore various expedients have been used formaking ready to provide such differentiation in pressure, 'but thesehave usually involved operations subsequent to formation of the rubberprinting plate, and have involved procedures making accuratelycontrolled differentiation in amount and location of pressure difficultto obtain. Accordingly, among the several objects of this invention maybe noted the provision of `a method of making rubber printing plateswhereby the plates are made ready (i.e., formed so as to provide forpressure differentiation between large and small printing areas) duringthe production of the plates;

`and the provision of a method such as described which,

in economical manner as regards time and materials, enalbles accuratebuilt-inmake-ready control. Other objects and features will be in partapparent 'and in part pointed out hereinafter.

'Ihe invention accordingly comprises the methods hereinafter described,the scope of the invention being indicated in the following claims.

In the accompanying drawings, in which one of various possibleembodiments of the invention is illustrated,

FIG. 1 is a plan of a so-called master metal engraving;

FIG. 2 is a section on line 2-2 of FIG. l;

FIG. 3 is a View similar to FIG. 2 showing ho'w a socalled matrix ismade using the master engraving;

FIG. 4 is a plan of the matrix;

FIG. 5 is a half-section in perspective of the FIG. 4 matrix;

FIG. `6 is a view of a so-called stencil sheet or template used in themethod of this invention;

FIG. 7 is a section showing certain initial steps in the formation of arubber printing plate 'according to this invention, using the matrix ofFIGS. 4 and 5 and the stencil sheet of FIG. 6;

FIG. 8 is a view of the printing face `of the completed rubber printingplate;

FIG. 9 isa view of the other face (or back face) of the completed rubberprinting plate; and,

FIG. l is a half-section in perspective of the rubber printing plate ofFIGS. 8 and 9.

Corresponding reference characters indicate cor-responding partsthroughout the several views of the drawings.

Referring to FIGS. l and 2 of the drawings, there is indicated at 1 whatis referred to as a master engraving. As shown, this consists :of Iarectangular metal plate, for example, which has one face routed out asindicated at 3 to provide a desired printing pattern in relief, and aperipheral retaining wall all around the plate. For purposes ofsimplified illustration, the printing pattern is 31,103,168 PatentedSept. l0, 1963 ICC shown las comprising two relatively large printingareas, a square area 7 and a circular area 9, and two relatively smallprinting areas, a tine-line area 11 `and a dot 13. 'Ihis is illustrativeof conventional printing patterns which will include designs,trademarks, etc. The master engraving 1 is made in well-knownconventional manner. The routing at 3 may be ,uniform in depththroughout, corresponding to the thickness in relief desired for theprinting areas on the printing face of the rubber printing plate to bemade. The master engraving 1 is also sho-wn as formed with grooves lasindicated at 15 and 17 for forming centering lines 15a and 17a (seeFIGS. 4 and 5) in a matrix 19 (see FIGS. 4 and 5) to be made using themaster engraving.

As shown in FIG. 3, the matrix is made using master engraving 1 inconventional manner by packing a thermosetting resin powder as indicatedat 21 into the routed cavity 3 in the master engraving, and covering thefaces of peripheral wall 5 yand of areas 7, 9, 11 and 13 with thispowder to a predetermined depth. The powder may be a phenol-formaldehyderesin powder `such as sold under the trade designation Bakeliteconventionally used for making such matrices. A plate 23 ofthermosetting resin is applied over the powder. This plate lmay be 'aplate of phenol-formaldehyde resin such as sold under the tradedesign-ation Bakelite conventionally used `for making such matrices. Itwill be understood that a parting compound |will usually be applied tothe master engraving to enable the matrix to be stripped from theengraving. Heat and pressure :are `applied to set and cure the resinpowder and bond it to plate `2.3, thereby to form a matrix 19 havingimpressions in reverse of relief of the printing areas 7, 9, 11 and 113of the master engraving. Referring to FIGS. 4 and 5, the impressions orcavities in the matrix 19 are respectively designated 7a, 9a, 11a and13a. 'Ihese are all of substantially the same depth. By reason of theprovision of grooves 15 and 17 in the master engraving, centering lines15a and 17a are formed `as ridges on the matrix 19. FIGS. 4 :and 5 showthe matrix 19 stripped from the master engraving 1.

As shown in FIG. 6, a so-called stencil sheet or template 2S is preparedhaving openings 7b land 9b corresponding in outline to the large areas 7and 9 of the master engraving 1 and to the large areas 7a and 9a of thematrix 19, but without any openings corresponding to small areas 11 and13. This sheet or template may be made of paper, sheet metal, or 'anyother suitable material, and may be easily :and 'accurately preparedsimply by taking an ink impression (a proof) on the stencil sheet crtemplate off the master engraving 1, then cutting out the areas printedon the sheet or template by contact with ink on areas 7 and 9 of themaster engraving. Centering lines 15b and `17b are marked on the stencilsheet or template, being accurately located thereon relative to openings7b and 9b from grooves `15 and 17 of the master engraving.

As shown in FIG. 7, strips 4of unvulcanized rubber R are placed in thecavities 7a and 9a of the matrix, and over these cavities and otherportions of the matrix. Strips of unvulcanized rubber may also be placedover cavities 11a and 13a. A backing plate 27 is applied over rubber Ron the matrix. This backing plate 27, as iappears in FIG.' 7, mayconsist of la piece of fabric 129 having layers -31 and 33 [ofunvulcanized rubber on both faces thereof. Layer 31 is shown as thickerthan layer 33, and layer 31 is applied face down over rubber R on thematrix. It will be understood that a suitable parting material isapplied to the matrix prior to application of rubber R and the backingplate 27. The rubber used at R and in plate 27 may have a durometer inthe range from 20-80, for example. Also yas shown in FIG. 7, stencil'sheet or template 25 is applied lover the backing plate 27, and iscentered -by registering lines 15b and 17b on the stencil sheet ortemplate with lines 115@ and 17a on the matrix so that openings 7 b and9b in the stencil sheet or template register at least approximately (ifnot perfectly) with cavities 7a and 9a in the matrix. The stencil sheetor template is substantially thinner than the rubber. f

Then, the :assembly of the matrix 119, rubber R, backing plate 27 andstencil sheet or template 25 is placed in a vulcanizing press, and heatand pressure are applied to cause lling of the cavities 7a, 9a, 11a and13a inthe matrix with rubber (from strips R, possibly Ialso some rubberfrom layer 31 of the backing plate), also to cause filling of theopenings 7b and 9b of the stencil sheet or template with rubber fromlayer 33 of the backing plate, bonding of the rubber in the cavities ofthe matrix with the backing plate, and vulcanization of the rubber. Itwill be understood that the pressure causes squeeze-out of rubber fromlayer 33 into fopenings 7b 'and 9b lof the stencil sheet or template,the rubber leveling off flush with the outer face of the template. Thisresults in formation of the rubber printing plate 35 shown stripped fromthe matrix in FIGS. 8-10, and lwith stencil sheet or template 25removed, having the printing pattern comprising printing areas 7c, 9c,11C and 13C (corresponding to areas 7, 9, -11 and 13 fof the masterengraving) on its printing face (see FIGS. 8 and 10), and integralraised areas` 7d and 9d ion its other face (see FIGS. 8 and 9). Areas 7dand 9d correspond in outline to and are at least approximately inregister with lareas 7c and 9c. The faces of areas 7d and 9d are offsetlfrom the back face of plate 35 by an amount equal to the thickness ofthe stencil sheet or ternplate 25, and the amount of this offset may bemade as desired by using a stencil sheet or template of appropriatethickness. When the plate 35 is used on the printing cylinder of aprinting press, for example, raised areas 7d and 9d effect impression ofink on the work over areas 7c and 9c at higher pressure than over areas11e` and :13e (the latter not being Ibacked yby `any raised areas). Thedifferentiation in pressure may be accurately controlled in `amount bysuitable preselection of the thickness of the stencil sheet or templateto determine the thickness of raised areas 7d and 9d and is accuratelycontrolled as to to location as will be'evident.

It will be understood that a rubber printing plate may be made inaccordance With the invention 'with raised areas of different thicknesslon the back of the plate by using a plurality of appropriate stencilsheets or templates of different thickness to provide the desireddilferentiation in thickness of the raised areas. In this manner,variable pressure may lbe obtained on different printing areas of thesame platerfor proper impression [of all the printing areas.

In view of the above, it will be seen that the several objects of theinvention are achieved land other advantageous results attained.

As various changes could be made in the above methods without departingfrom the scope lof the invention, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is .claimed is:

1. The method of making a made-ready rubber printing plate having on theprinting face thereof a printing pattern in relief in rubber, saidpattern having iirst and second printing areas as to which higherprinting pressure is required for the first than for the second forproper printing impression, said method comprising forming a matrixhaving an impression of said pattern in reverse of relief with the areasthereof corresponding to both said irst and second printing areas ofsubstantially the same depth, applying unvulcanized rubber over thematrix, applying over the back ofthe rubber a fiat template which issubstantially ythinner' than 4the rubber, said template being of suchoutline and so positioned relative t0 the matrix as to leave uncoveredby the template an area at the back of the rubber having a boundary suchas to circurnscribe the boundary of the irst printing area Whilecovering a portion of the back of the rubber in register with saidsecond printing area, applying heat and pressure to the rubber to moldthe rubber in the matrix to form the printing plate and to vulcanize therubber, pressure being applied against the template to cause the rubberto lill the areas of reverse relief in the matrix thereby .fro form saidprinting pattern in relief in rubber at the printing face of theprinting plate, With substantially uniform projection of the entireprinting pattern in relief from the plate at its printing face, and tocause the uncovered rubber at the opposite face thereof from the matrixto level off iiush with the outer face of the template, thereby to formoffset rubber areas at the back of the plate with the area of the rubberlying beneath the template at the back of the plate inwardly offset fromthe area of the rubber levelled `off with fthe outer face of thetemplate at the back of the plate a distance corresponding to thethickness of the template, and stripping the template from the back ofthe plate.

2. The method of claim l wherein the template is consti-tuted by a sheethaving an opening therein of such outline as to circumscribe said firstprinting area, and is applied over the rubber with said openingsubstantially in register with said first printing area.

3. The method of claim 2 wherein the matrix and template are formed withcorresponding centering lines and the template is positioned over therubber with said opening therein substantially in register with saidfirst printing area by registering said lines.

References Cited in the file of this patent UNITED STATES PATENTS1,947,986 Harley Feb. 20, 1934 2,026,021 Danser Dec. 31, 1935 2,088,399Gibson July 27, 1937 2,182,802 Frazier Dec. 12, 1939 2,789,500 ReillyApr. 23, 1957 2,814,990 Myers Dec. 3, 1957

1. THE METHOD OF MAKING A MADE-READY RUBBER PRINTING PLATE HAVING ON THEPRINTING FACCE THEREOF A PRINTING PATTERN IN RELIEF IN RUBBER, SAIDPATTERN HAVING FIRST AND SECOND PRINTING AREAS AS TO WHICH HIGHERPRINTING PRESSURE IS REQUIRED FOR THE FIRST THAN FOR THE SECOND FORPROPER PRINTING IMPRESSION, SAID METHOD COMPRISING FORMING A MATRIXHAVING AN IMPRESSION OF SAID PATTERN IN REVERSE OF RELIEF WITH THE AREATHEREOF CORRESPONDING TO BOTH SAID FIRST AND SECOND PRINTING AREAS OFSUBSTANTIALLY THE SAME DEPTH, APPLYING UNVULACANIZED RUBBER OVER THEMATRIX, APPLYING OVER THE BACK OF THE RUBBER A FLAT TEMPLATE WHICH ISSUBSTANTIALLY THINNER THAN THE RUBBER, SAID TEMPLATE BEING OF SUCHOUTLINE AND SO POSITIONED RELATIVE TO THE MATRIX AS TO LEAVE UNCOVEREDBY TE TEMPLATE AN AREA AT THE BACK OF THE RUBBER HAVING A BOUNDARY SUCHAS TO CIRCUMSCRIBE THE BOUNDARY OF THE FIRST RPRINTING AREA WHILECOVERING A PORTON OF THE BACK OF THE RUBBER IN